Comment 0 for bug 1819875

snapd: 2.37.2
Ubuntu 18.04
core snap: 6405
kernel: 4.15.0-29-generic

Preconditions:
 Snap updated base from core16 to core18
 Snap has one or more services

Expected result:
 snap refreshes to new revision using new core18 base

Actual result:
 snap refresh to new revision fails as it is using still core16 base
 post-refresh hook fails as executables from snap package fails to run against wrong glibc
 if there is no post-refresh hook snap refreshes to new revision, but services do not start for same reason of glibs mismatch

Closer look revealed that service forked additional long running process which was dangling around and was preventing successful unmount.
While best is to define additional process as service to provide better way to control it's lifecycle, we probably still need more aggressive process control/kill when moving between snap revisions so we are not keeping dangling services from previous revisions